Check on the chart what the gradient is, so if you have gradient of 5.6% for example multiply that by 0.6 and you get 3.36 FPA.
Now for selected VOR approaches we generally use 3.0FPA unless it is a real steep approach in which case you check the above gradient and start calculating from the threshold upwords.
For example you want to cross the threshold at 50' so 1 nm before the threshold you want to be 50'+ 336' (converted fpa) = 386', 2 nm before threshold 386'+336=722' and so on until you go back to FAF. However if you do it this way make sure your altitudes meet any restrictions on the chart.
All the best